Can I add kern/28582 to the list?
Basically on machines that don't have PS/2 ports, you can't debug
without disabling pckbc and pckbd in userconf, or building your own
kernel with them removed because pckbd always attaches as console
even when there are no physical PS/2 ports due to legacy emulation
which cannot be turned off.
But, building a kernel without pckbd/pckbc means you can't use the
BIOS emulation to debug post boot before the USB controllers get set
up, before ukbd gets attached, or get to userconf.